In one aspect this invention relates to explosive containers. In another aspect, this invention relates to an improved explosive device for delay activated explosives which are to be detonated by a detonator cord. In a further aspect, this invention relates to an explosive device for delay activating explosives which protects against premature detonation of the explosives.
In blasting, insensitive explosives or blasting agents such as ammonium nitrate-fuel oil compositions, for example, are detonated by booster or primer charges containing high explosives sensitive enough to be detonated by ordinary blasting caps. For safe and efficient use, the detonation of the primer charges used to initiate such blasting agents must be capable of being precisely timed and must be highly reliable. While electric blasting caps have the advantage of precise timing, the premature detonation of electric caps by thunderstorms, stray electric currents, static electricity or RF energy, has caused the industry to look to other means of detonating primer explosives, such as the use of nonelectric blasting caps in combination with millisecond delay fuses employing known pyrotechnic materials.
U.S. Pat. No. 3,420,173, issued to Slawinski, Jan. 7, 1969, discloses an axially expandable container defining grooves therein for receiving a detonator cord or a blasting cap held in place by a tubular sleeve disposed about the container. A similar device is taught by U.S. Pat. No. 3,789,760, issued to Griffiths, Jan. 5, 1974, wherein a plastic or cardboard sleeve defines a series of channels through which a detonator fuse may be threaded and blasting caps inserted to detonate the primer. A disadvantage associated with these types of devices, however, is that the energy released by the burning detonator cord adjacent to the container may be sufficient either to blow a hole in the container, causing the primer to malfunction, or detonate the primer prematurely. Another means for coupling the blasting cap to the outside of explosive cartridges is to separate the detonator fuse from the container by an energy absorbing media. Such a primer device is taught by Kern in U.S. Pat. No. 3,431,849, issued March 11, 1969. Even these devices, however, are not completely reliable, because, although they may prevent the energy released by the detonator fuse from prematurely exploding the container, the explosive force may nevertheless be sufficient to separate the sleeve and the blasting cap from the container, resulting in malfunction.
Thus, there is a continuing need for an explosive device which provides for delayed detonation of an explosive container using detonator cord means.
The present invention is directed to an explosive device for delay activated explosives which are to be initiated by a detonator cord. The explosive device of the present invention overcomes the deficiencies of the devices described above in that highly reliable timed delay detonation of explosive materials in a container is achieved by providing for: (1) initiation of a delayed detonator for the explosive container, (2) separation of the detonator from the detonating cord so as to prevent premature detonation, and (3) retention of unitary contact between the explosive container and the detonator after initiation thereof by detonating cord. According to the invention, a novel explosive device is provided for use with delay actuated explosives, which comprises:
an explosive container having a detonator cord receiving conduit and a detonator receiving well along an outer surface thereof and offset from the detonator cord receiving conduit; and
a detonator delay unit having an initiating means communicating with the delay detonator means the delay unit being adapted in a manner so that the initiating means can be positioned proximate to the detonator cord conduit of the container when the delay detonator means is positioned within the detonator receiving well thereof.
The term "offset" as used herein is defined to mean that the detonator cord conduit and the detonator receiving well are not adjacent on the explosive container but rather are spatially separated on the periphery thereof in a manner such that the distance between them is sufficient to prevent premature detonation of the detonator as a result of the thermal and explosive energy of the detonating cord passing through the detonation cord conduit. The detonator receiving well of the explosive container is preferably located longitudinally along the outer periphery thereof but can be located on any outer surface of the container including an outer surface in the shape of a tube, for example, extending into the interior of the container having a closed end so as not to communicate with the interior of the container.